These days, high integration of LSI promotes miniaturization of circuits inside the LSI. The miniaturization decreases a cross-section of wiring line and a distance between adjacent wiring lines. Thus, the miniaturization increases wiring resistance and wiring capacitance inside the LSI. As a result, wiring delay determined by the wiring resistance and the wiring capacitance increases to make it difficult to more speed up the LSI. Optical interconnection technology draws attention as a technology to solve the wiring delay involved in the high integration of the LSI. The optical interconnection technology employs optical waveguides to transmit optical signals, and eliminates an increase in the wiring resistance and wiring capacitance involved in the miniaturization mentioned above. A disclosed optoelectric LSI transmits signals using such optical interconnections.
The optoelectric LSI includes several functional blocks to electrically perform signal processing, and optically transmits signals among the blocks. The optoelectric LSI needs a light emitting element for converting processed electric signals into optical ones and a light receiving element for converting transmitted optical signals into electrical ones. Semiconductor lasers are employed as a conversion element to convert electric signals into optical ones. Examples of the semiconductor lasers include an end surface emitting laser, a vertical cavity surface emitting laser (VCSEL), and a micro ring laser, reportedly operating in a GHz band.
Known integration of semiconductor lasers and optical waveguides includes the following configurations:
(1) a laser structure is integrated on optical waveguides by wafer bonding;
(2) a laser structure and optical waveguides are bonded to each other via an organic film; and
(3) a laser structure and optical waveguides are directly mounted on a Si wafer. The configuration (1) cannot efficiently remove heat generated at the laser structure because the configuration includes an air space under the laser structure. The configuration (2) cannot efficiently remove heat because of the laser element formed on the organic film. In addition, the configuration (2) makes it difficult to efficiently couple light outputted from the laser element to the waveguides because of the organic film laid between the laser element and the optical waveguide. In contrast, the configuration (3) is likely to efficiently remove heat because both the laser structure and optical the waveguides are formed on the Si wafer. Alignment accuracy is, however, needed for the configuration (3) to align laser elements to the waveguides, and the elements are each mounted on the Si wafer, thereby causing a problem of mass production.
Accordingly, it is desired to form light emitting and receiving elements on a Si wafer without using a less thermally-conductive layer, such as an air layer and an organic material, etc.